Rare Occurrence of Anti-A₁ Antibody in an Infant with A₂B Blood Group

Dear Editor,

We report a case of an infant with a diagnosis of urachal cyst and blood group A₂B RhD positive with anti-A₁ antibodies in the serum. Anti-A₁ antibody is not considered clinically significant as it is usually IgM in character, reacting at room temperature (R.T.) or 4 °C. In the index patient, anti-A₁ antibody was IgM in nature reacting at AHG phase.

A blood requisition of a nine-month old female, with a diagnosis of urachal cyst was received for a packed red blood cell unit, as a surgical excision was planned. Her hemoglobin was 7.1 g/dl. The results of infant’s blood grouping (CTT- conventional tube technique) are shown in the Table 1. As there was a blood group discrepancy in cell and serum grouping, further immunohematology work up was done. Reaction with anti A₁ lectin (Dolichus bifloris, Tulip Diagnostics, Goa) was negative. Reaction with anti-H lectin (Ulex europaeus, Tulip Diagnostics, Goa) was positive (3 +). Serum grouping with A_cell was 2 + at I.S. (immediate spin) and 1 + at AHG (antihuman globulin) phase. The corresponding reaction by column agglutination gel technique (CAT) (BioRad Switzerland) was 4 + (saline IgM) and 2 + (IgG + C₃d AHG) phase. There was no previous history of transfusion. Medication history included administration of injectable ceftriaxone.

Table 1.

Patient’s blood group (CTT)

Anti- A	Anti- B	Anti- D	Anti- AB	Acell	Bcell	Ocell	Auto control
Cell and Serum Grouping (CTT)
3 +	4 +	4 +	4 +	2 +	Negative	Negative	Negative

	I.S	4 °C	37 °C	AHG
Serum grouping (CTT): (At different temperatures and phases)
Acell	2 +	4 +	1 +	1 +
Bcell	Negative	Negative	Negative	Negative
Ocell	Negative	Negative	Negative	Negative
Auto control	Negative	Negative	Negative	Negative

Autocontrol of the patient was negative by CTT and CAT. Antibody screen (CAT) showed negative results. Dithiothreitol (DTT) treatment of the serum (along with PBS phosphate buffered saline as control), was done to determine immunoglobulin class of anti-A1 antibody. Post DTT treatment of serum, reaction with A₁ cells was negative at saline and AHG phase by gel technique (CAT), confirming the antibody to be immunoglobulin (Ig) M type. The blood group was finally interpreted as A₂B RhD positive with naturally occurring anti-A₁ antibodies in plasma. The anti-A₁ antibodies were present in a titre of 1:2 at I.S. and AHG phase (CTT), were IgM in nature, reacting at 37 °C and at AHG phase.

One B RhD positive packed red blood cell (prbc) was transfused to the patient uneventfully. The next compatible blood group PRBC unit was preferred to avoid any hemolytic transfusion reaction episode due to anti-A₁ antibodies which were reacting at 37 °C and at AHG phase, hence clinically significant. Mother’s blood group was A₂B RhD Positive and anti-A1 antibody was not present in her serum. Father’s blood group was B RhD Positive.

Literature on frequency of A₂B blood group is limited. In a study by Ying et al. on 11,263 Chinese individuals, A₂B blood group was found in 3.83% (98/2556) of all AB individuals, 0.8% of the whole cohort [1]. A study from India quoted the prevalance of 6.6% (2667/40,113) of AB blood group individuals and 0.7% (280/40,113) of A₂B group [2]. Another study from India reported the prevalence of AB as 5.27% and that of A₂B as 1.43% among 150,536 blood donors [3].

A₂B individuals may sometime demonstrate anti-A₁ antibody (22–35% in Caucasians) but it is extremely rare in infants [4]. In the study by Shastry et al., out of 280 A₂B individuals, 40 were neonates but none had anti-A₁ antibody in the serum [2]. One out of 98 A₂B individuals demonstrated anti-A₁ antibody in the above quoted study from China. [1] There is a documented report of anti-A₁ antibody in infant among 10,000 blood samples [5]. This case is of interest because of extremely rare occurrence of anti-A₁ antibody in infants.

Authors Contribution Statement

Malhotra—Study design, Acquisition, analysis, or interpretation of data, Drafting of the manuscript, Critical revision of the manuscript for important intellectual content, Statistical analysis. Jain—Study concept and design, Acquisition, analysis, or interpretation of data, Drafting of the manuscript, Critical revision of the manuscript for important intellectual content, Statistical analysis, Administrative, technical, or material support, Study supervision. Sharma—Study concept, Acquisition, analysis, or interpretation of data, Critical revision of the manuscript for important intellectual content, Statistical analysis, Administrative, technical, or material support, Study supervision.

Data Availability

The data can be obtained from the first/corresponding author upon reasonable request/Ethics permission.

Declarations

Conflict of interest

This authors declare no conflict of interest.

Patient Confidentiality

Patient confidentiality was maintained while writing the manuscript. No identifying information was revealed.